Writing in the journal Scientific Reports, the team of scientists from Sweden were able to see into the past and work all this out by carefully picking apart the layers of the crystals formed within the magma chamber that was beneath Toba all those thousands of years ago.
You see, when crystals form within magma, they move around a lot, through different parts of the chamber and across a range of temperatures, pressures, and chemical compositions. As they cool, different layers form around their edges that record the conditions of the magma they were swimming through at the time.
“Quartz crystals that grow in the magma register chemical and thermodynamical changes in the magmatic system prior to eruption, similar to how tree rings record climate variations,” lead researcher David Budd, a geophysicist at Uppsala University, said in a statement.
The crystals within Toba appear to indicate that, just before the eruption took place, a new source of magma – one full of water – was injected and absorbed into the primary source of molten doom.
The surrounding rocks fit the bill, and the researchers concluded that the magma must have been able to annihilate and subsume much of the rocky magma chamber just prior to the volcanic fireworks that took place.
A NASA Landsat image of Lake Toba today, the rough outline of the crate left behind by the 73,000 event. NASA
Toba’s cataclysm registered as an 8 on the Volcanic Explosivity Index (VEI), the maximum value on the scale. This type of eruption is extremely rare - as far as volcanologists can tell, there have only been 42 in the last 36 million years.
We are “due” for another, though. All eyes are on Campi Flegrei beneath Naples, or the infamous Yellowstone caldera.